The expression is
.
The general factor trinomial form is
.
In the above trinomial,
.
Since c is positive and b is positive, you need to find two positive factors with a sum of 15 and product of 36.
\Make an organized list of the factors of 36, and look for the pair of factors with a sum of 15.
\
Apply the pattern form:
when
.
because
.
The factor form of expression is
.